This project is designed to determine if the frequency and character of rat vocalization changes as a function of social experience. Two populations of rats will be compared: One population will be trained to engage in cooperative behavior patterns to satisfy food and water requirements. The other population will serve as an experimental control group and will not be required to perform cooperative behaviors. It is expected that as each population triples in size those rats require to perform cooperative behaviors will exhibit a larger repertoire of vocal patterns than will the control group, while crowded control rats will exhibit vocalizations of diminished complexity.